Wireless communication systems typically use power amplifiers to amplify signals prior to over the air transmission. The efficiency of a power amplifier generally impacts the performance of devices such as mobile phones and base stations. Envelope tracking provides significant advantages in terms of minimizing power consumption in the power amplifiers and this can have a significant impact on thermal aspects of the devices and on battery life. Envelope tracking systems provide a variable voltage level to a power amplifier (PA) to ensure that the PA is operating at an optimum efficiency for a given instantaneous output power requirement. Envelope tracking systems typically comprise one or more operational modes and a transition between the different operational modes is essential for the efficient operation of the power amplifier.